Avoid using Z_RLE and Z_FIXED with old zlib versions that don't support them.

diff --git a/coders/png.c b/coders/png.c
index d53265b51f7d3ab526359c0df6d18b12b715df14..1abebc378853f2238f336def94ec66b7baeebf2f 100644 (file)
--- a/coders/png.c
+++ b/coders/png.c
@@ -11053,10 +11053,18 @@ static MagickBooleanType WritePNGImage(const ImageInfo *image_info,
         mng_info->write_png_compression_strategy = Z_HUFFMAN_ONLY+1;
 
       else if (LocaleCompare(value,"3") == 0)
+#ifdef Z_RLE  /* Z_RLE was added to zlib-1.2.0 */
         mng_info->write_png_compression_strategy = Z_RLE+1;
+#else
+        mng_info->write_png_compression_strategy = Z_DEFAULT_STRATEGY+1;
+#endif
 
       else if (LocaleCompare(value,"4") == 0)
+#ifdef Z_FIXED  /* Z_FIXED was added to zlib-1.2.2.2 */
         mng_info->write_png_compression_strategy = Z_FIXED+1;
+#else
+        mng_info->write_png_compression_strategy = Z_DEFAULT_STRATEGY+1;
+#endif
 
       else
         (void) ThrowMagickException(&image->exception,